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How exactly is the free shaft part of a gas turbines controlled?

As you can see in the picture, the free turbine still gets the same exhaust gas that the main turbine gets.

How can it exactly spin freely from the main turbine?
How can the free shaft even stay stationary while the main turbine is spinning at high rpm even though it is still exposed to the same exact exhaust gas flow which makes the main turbine rotate?
Why does the exhaust gas also not rotate the free shaft?
Does the free shaft have a clutch attached to it or something that disconnects it from the driven wheel or the propeller so that wheel or propeller can stay stationary even if engine itself is spinning at high rpm?

I also read that gas turbine engines can act as a clutch or a fluid coupling exactly because of the fact that free shaft can operate freely from the main turbine. Chrysler, for example, in their turbine car removed the torque converter from the TorqueFlite automatic transmission that was attached to the gas turbine because gas turbine itself could act as the torque converter and therefore didn't need a separate torque converter to disconnect the engine from the output shaft.
How exactly is this "free spinning shaft" action accomplished?

A little bit of formatting and suddenly it's readable. Also, e.e. cummings gets away without capital letters. The rest of us, not so much.

The free turbine is literally just a windmill that generates torque when the wind blows on it. You could actually just stick it outside the engine itself behind the tailpipe and it would do the job, although way less efficiently.
The wind is provided by the "gas generator" on a turboprop, or the "core" engine on a turbofan. The torque is created from aerodynamic lift on the blades by the air blowing by, so stalling unstalling has a huge effect on the torque that can be produced.
When the blades are stationary and air starts to flow past the blades, the blades are mostly stalled and produce little lift and therefore little torque.
You can hold the propeller blade of a PT-6 turboprop with your hand to prevent the free turbine from spinning, and start the engine and let it run at ground idle while you hold the blade still (this is done all the time for maintenance purposes, normally using a restraint device like a special strap).
As long as you don't let the blades move, the torque force you have to resist from the mostly stalled turbine blades is very light.
Let the propeller move however, and the blades start to unstall and turbine starts to generate high torque, and you were holding it, you would have to let go and get out of the way.
So as far as controlling it, it's simply a matter of controlling how hard the wind is blowing, which means controlling the flow through the gas generator/core with the normal jet engine controls (regulating fuel flow).

It'll be optimized for the engine's operating requirements and conditions to get the most MPG and power where you want it.  You would more or less seek to get the most lift over drag from the blade at the desired operating RPM and gas flow rate, so whatever angle gets you there.  It's not a big problem for an airplane engine that runs at a constant RPM all the time; more of a challenge for, say, a turboshaft that needs to produce decent torque over a speed range, like the Lycoming engine in the Abrams tank.

@JohnK: A land-vehicle turboshaft will still operate in a fairly-narrow speed band, though; almost all of the variation in wheel speed (or all of it, if turboelectric) is taken up by the transmission.

To answer the questions:

“How can it exactly spin freely from the main turbine?”

The free shaft i.e. the power turbine is not connected mechanically to the gas generator spool and can turn at independent speeds or even independent directions from the gas generator spool.  Typically the power turbine shaft connects directly into a gearbox, which either drives a propeller, in the case of a turboprop, or a rotor in the case of a turboshaft engine.

“Does the free shaft have a clutch attached to it or something that disconnects it from the driven wheel or the propeller so that wheel or propeller can stay stationary even if engine itself is spinning at high rpm.”

In aviation applications, there is no clutch between the propeller or rotor transmission gearbox.  The fact that the shaft is not linked to the gas generator shaft is what allows it to operate as a fluid clutch.
The power turbine and drive shaft does not need to be mechanically linked to the gas generator spool in order to generate mechanical power, provided the exhaust gases moving over the power turbine undergo a sufficient drop in enthalpy, transferring their energy into mechanical work.  In short, the power turbine spins for the same reason as the gas generator turbine section does.

“How can the free shaft even stay stationary while the main turbine is spinning at high rpm even though it is still exposed to the same exact exhaust gas flow which makes the main turbine rotate?”

Consequently the power turbine could be mechanically locked stationary while the gas generator continues to operate (provided this does not exceed either the thermal or torque limits of the driveshaft and reduction gearboxes).

“Why does the exhaust gas also not rotate the free shaft.”

The exhaust gases DO rotate the free shaft.  See my answer above.
I can’t comment on the drive system for the experimental Chrysler car, but one of the few land applications of turbine engines, the power pack for the M1 Abrams main battle tank, I believe uses a clutch between the power turbine driveshaft and the tank’s transmission.

Related good reading.  Could variable pitch turbine power out blades be possible?

"one of the few land applications of turbine engines" Wouldn't nearly all electric power generators used on the grid aside from PV-based solar installations also be land-based turbine engines?

So be it………………..


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Is it legal to start a non-profit that anyone can donate to which can pay the expenses for donated medical/animal transport flight?
I know this is a question that a lawyer should be helping out with, but I figured I would start here just to point me in some different directions.
I am interest in doing flights to ferry passengers in need of transportation to medical appointments or animals in need of transport for rescue. i.e. Pilots for Patients, Angel Flight, Pilots N Paws. I'd like to do this as often as possible but do not have the financial ability to pay the expenses for countless flights. I have some friends who are interested in donating to me to be able to do more of these flights so I was hoping to set up a non-profit to make these donations tax deductible. And then the non-profit could pay for the expenses of the flights or possibly even an hourly rate for my time.
If I have my commercial rating, is it ok to be reimbursed for flight expenses for these flights? Is it okay if I am paid beyond the expenses of doing these flights?
My dream goal would be to eventually grow this concept to include other pilots, have a fleet of planes, etc, but trying to start with just myself for now.
Thanks for any help

If you have bona fide friends that want to gift you some money because they like you and you want to spend that money on charitable flights the FAA doesn't need to know about it. ;) (Needless to say this wouldn't be tax deductible).

It sounds to me like you would be holding out a willingness to transport people from place to place for compensation. This makes you a common carrier, and you would need an part 135 certificate.
If you want to fly charitable flights, fly the charitable flights you can afford to fly.
Alternatively, you could ask the FAA to exempt your organization from some of the FARs under part 11. This will come with extra operating limitations, but they might be less onerous than a full-on part 135 operation. This is at the FAA's discretion. It's very unlikely that they will allow you to be compensated beyond your expenses, but you may get an exception for fuel costs.
To give you an idea of what this might be like, here is Angel Flight of NE's exemption letter. As you can see, it has a lot of requirements.
This is probably not allowed under tax law anyway. From How to lose your 501(c)(3) tax-exempt status (without really trying):

A 501(c)(3) organization’s activities should be directed toward some exempt purpose.
Its activities should not serve the private interests, or private benefit, of any individual or
organization more than insubstantially.

and

A 501(c)(3) organization is prohibited from allowing its income or assets to benefit
insiders – typically board members, officers, directors and important employees of an
organization. If an organization benefits insiders, the insiders and the organization could
be subject to penalty excise taxes and the organization could lose its tax-exempt status.

This is a commercial air operation, falling under Part 135. With a CPL, as well as meeting other requirements (hours), and with an operating certificate for the company, you may conduct it.
The FAA's definition of private flights is much stricter than the IRS' definition of non-profit. A non-profit pays wages, it just can't be used as the owner's personal wallet. Most non-profits aren't charities.
For the FAA, any flights where the pilot earns any money, or even just doesn't pay for the expenses, are commercial. Whether it comes from a for-profit, non-profit, or a private person is immaterial.
What you're devising is a FAA Part 135 Air Carrier, which requires commercial certification. It may qualify for tax exemptions, but that's an aviation-unrelated matter that can be better resolved on Law or Finance SE.

Just a CPL isn't enough. You need an operating certificate or to be operating under someone who has one, and there are additional requirements to be part 135 PIC (namely, 500 total hours, 100 XC hours, 25 night XC hours, and an instrument rating).

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What are the differences among ETO, ETA, and ELDT?
We are analyzing the Arrival Manager (AMAN) logs and would like to have an understanding of the difference between Estimated Time for Arrival (ETA), Estimated Time Over (ETO), and Estimated Landing Time (ELDT). Are they calculated based on different reference points?

Please help us understand the question better by defining your acronyms.

Thanks Michael for your suggestions. Here are the definitions of my acronyms. ETA: Estimated Time for Arrival, ETO: Estimated Time Over, ELDT: Estimated Landing Time. Those Acronyms are from the Arrival Manager (AMAN) system, not sure if they are standard lingos among other systems, or specifically defined for the AMAN system.

ETO is the estimated time over a certain point, probably some sort of arrival fix defined in your AMAN, such as the beginning of the arrival route.
ETA is the estimated time over the initial approach fix or overhead the aerodrome.
ELDT is the estimated time of crossing the threshold of the landing runway.

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Why are fighter jets so loud when doing slow flight?
Going to air shows I noticed that when fighter jets did slow fight, it was just as loud as high speed passes. Why is this?

Ignoring everything else, a slow pass is ... well slow, it takes longer.  Is 100 decibels for 0.1 seconds actually "louder" than 90 for 2 seconds, in terms of perception?

In order to understand why engine noise and speed are at best loosely correlated, consider these two extremes: airplane is diving straight nose down with engines off: zero engine noise, high speed. And the airplane is hovering without moving at all: lots of engine noise, because there is no lift and the engine needs to use a lot of power just to fight gravity, but the speed is zero.

Fighters have low bypass engines compared to airliners.  That means the exhaust comes out much faster than on airliners making a lot more noise.  It is also why fighters have a much higher pitch to the engine noise.

When fighters are going slow they still need to generate enough lift to maintain level flight.  This is done by increasing the angle of attack, and coincidently 100% of the time the induced drag also increases. (but don't confuse this with a cause/effect relationship!)
As induced drag increases, more thrust is needed to overcome it.  This is called operating on the "backside of the power curve".  At some point almost full power is needed just to overcome the drag and maintain level flight, which is why you hear the noise.
There are lots of questions and answers dealing with drag curves that will help you understand this on a deeper level if you are interested.

Don't think of slow flight as the same as driving slowly in your car. Think of it as driving your car up a very steep mountain - you will slow down, yes, but you will also need to rev your engine up on low gear.

What is the motivation for saying that operating at very high angles-of-attack does not actually cause the associated increase in induced drag?

@slebetman-- actually-- the car makes less drag, and requires much less power, going slower than going faster.  With no exceptions.  What you are talking about is just a gearing/motor rpm issue, which basically doesn't exist in airplanes, and certainly not in pure jets.  (And also not in electric cars!)

@quietflyer, motivation for that phraseology is to keep the aero PHDs who insist there’s no cause and effect relationship off my back.  ;)

@quietflyer it requires much more power if the reason it is going slowly is that it is going up a steep mountain!

@quietflyer hence why the analogy was the slope of the mountain and not the speed of the car!

@quietflyer I'm not sure what is so difficult about "think of slow flight as climbing a hill, not as driving slowly" for a layperson. Yes, you aren't going up. So what? It's an analogy.

I have seen the claim that wake vortices somehow cause induced drag rightly disputed, but anyone wishing to dispute there being a causal dependency of induced drag on AofA should first consider what Peter Kämpf wrote in his 3rd. paragraph of https://aviation.stackexchange.com/a/5056/1981 : "The wing creates lift by deflecting air downwards. This happens gradually over the wing's chord, and creates a reaction force orthogonally to the local speed of air. This means the reaction force is pointing up- and slightly backwards. This backwards component is induced drag!" (my emphasis.)

@user253751 -- ok, so you are saying that when a plane flies slowly, it's like a car driving on a slope that is somehow automatically controlled to raise up steeper the slower the car goes.  Ok.. so 1) how does that give any real insight?  You might as well say that a drogue parachute is automatically programmed to open when the car goes slow, or the brakes are programmed to apply whenever the car goes slow.  2) If we say that a nose-high pitch attitude is somehow equivalent to climbing a hill

If we say that a nose-high pitch attitude is somehow equivalent to climbing a hill, then the logical conclusion is that we are most efficient with the pitch attitude as flat as possible-- which is not true in most cases.  Basically what I'm trying to say is that any analogy that misses the point that induced drag increases when we fly extremely slowly, regardless of the trajectory of the resulting flight path, is missing the main point.

Ok guys, please take the automotive metaphor over to chat - this is not productive or particularly insightful...

This regime has a name on the "Power Curve", it's called the "Region of Reverse Command". It's called that because as the aircraft goes below a certain speed, it requires an increasing amount of power the slower you go to retain the same amount of lift.
Being in this area of the curve can be quite dangerous, and getting outside the backside of the curve is often referred to as "being behind the curve", and is actually something I think about somewhat frequently.
Story time:
I was out flying one day with my SO and two of our friends in a 172, it had a STOL kit and 160HP conversion, it also wasn't a particularly high density altitude day (this may have saved our lives). They really wanted to check out their house from above like most first-time plane rides. We cruised up there and they called their kids out of the house to come wave from the cul-de-sac.
In order to loiter I set the plane up for slow flight like I'd practiced countless times (I actually really enjoy chugging around like this), tossed in some flaps (don't remember now how much exactly), and throttled back and pitched to bring 'er down into the laid back position that a plane takes at that point in the curve. As the speed slowed I laid into the throttle to keep us a handful of knots above stall and orbited the house for a few minutes while watching the altimeter like a hawk and they had a good ole time trying to yell out the windows.
Why would the plane's mods have saved our lives? Well, while I was above the required "safe" altitude for the area, one thing that I hadn't taken into account is how much the stall speed changes at the wing loading with 4 adults in the thing. If I hadn't had the extra headroom afforded by those mods, I may have gotten into a point in the power curve where powering out of the reverse control regime before hitting the ground wouldn't be possible. This realization is why it's indelibly burned into my mind.
This is one area of flight where remembering "pitch controls airspeed, and throttle controls altitude" can be a literal lifesaver.

Am I right in assuming a plane with a positive thrust-to-weight ratio simply has that "maximum power available" remain above the "power required" all the way down to zero airspeed, so that the risk of "not enough time to power out of reversed command regime" is not an issue?

This would actually be an interesting question to pose on the site. Thinking about it I could consider a few different possible answers which would differ if the aircraft had vectored thrust or not. because the amount of thrust against gravity at some alpha will vary inversely to the lift generated by the wings, I do think the curve would look quite different, but I do not think that it would completely remove the area below the reverse command region except maybe if there was vectored thrust or if it had a VERY high TtW ratio.

At very low speeds, with a high AOA (angle of attack), they are using a lot of the thrust to just hold it up in the air, rather than lift over the wings.
Also, the crowd likes it...:)

This is the elephant in the room. Those passes could be a lot quieter, but the pilots are trained to make a lot of noise when passing over the crowds, then quieten down as they leave the show area

@Richard, for a given thrust setting needed to fly at a certain airspeed, how would the pilot increase or decrease the noise?

@MichaelHall i guess pilot has option to increase drag and use different thrust setting for certain airspeed too. Let’s say full flap with huge drag and higher thrust setting to make more noise.

Well, you are free to presume that the goal is to make noise, but it is actually a slow flight demonstration and noise is simply a byproduct.  Pilots are just not "trained to make a lot of noise"...

The last airshow that I saw, ended with supersonic-capable jets in various formations and choreography.  Of course, they're forbidden from actually going supersonic, but to make the noise, they also create a lot of thrust.  The combination of afterburner and speedbrakes together, seems a bit odd until you realize what their goal really is.  It was also interesting to see a silent approach, and then a very short "fade-in" as one crossed in front of where I was.  Not a boom, but a very short fade from silence to very loud.

Much more impressive to the crowd would be slowly coming in, then revving up to full power in front of them and zooming away, I would think.

@user253751 - The F-22 Demo guy does exactly that. Slow walk down the showline (runway) at about 40mph, at about 750ft altitude. Apply more thrust, and rise up to the heavens.


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What is this indication on most turboprops?

What is the small fan I've seen on different turboprops?

This is the propeller synchronization (usually just called "prop sync") indicator, or "synchroscope." It rotates one way or the other to show the change in phase alignment of each propeller. During cruise, it's beneficial to manually or automatically (depending on aircraft) synchronize the frequency and often (again depending on aircraft) the phase of the blades to reduce noise and vibrarion (and consequently wear and tear).
In ancient times, before glass cockpits :), these were mechanical indicators with actual moving parts that rotated in response to the electrical signals from magnetic pickups mounted along the prop shaft.

Technically a prop synchrophaser.

@CarloFelicione The presence of a synchroscope doesn't mean a synchrophaser is installed, and synchroscopes don't show the phase alignment, only phase rate of change (equivalent to frequency difference). But yes, a device which aligns propeller phase in addition to frequency is properly called a synchrophaser.


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How can I control my airspeed using throttle to command?
I am developing code for a fixed-wing aircraft in ArduPilot to control desired airspeed and vertical speed through attitude commands (roll, pitch, yaw, and thrust) in simulation.
I understand the following:
1.Vertical speed is controlled through pitch.
2.Horizontal speed is controlled through throttle input.

However, I am having difficulty understanding the specific relationship between throttle input and airspeed. I have theoretical knowledge of Total Energy Control System (TECS), but I need to know how throttle adjustments directly affect airspeed.
Could anyone explain how airspeed is influenced by throttle input? Is there a mathematical relationship or formula that describes this interaction? Any detailed explanation or guidance would be highly appreciated.

"Could anyone explain how airspeed is influenced by throttle input?"  It isn't totally clear what you are asking for.  Yes, the primary pitch and power controls you referenced are correct and are taught as good pilot technique - but they aren't isolated from each other:  If you maintain altitude and add power you will accelerate.  Keep power constant and pitch and your vertical speed changes.  There are formulas that I will leave to the aero experts, but the short answer  is add power go faster, pull power go slower.  Just like in your car. (presuming front side of the power curve)

Best to think of the system in an energy-management framework. Pitch and throttle commands work together to effect a change in the state of the system. Not perfect but a helpful reference for this is https://www.faa.gov/sites/faa.gov/files/regulations_policies/handbooks_manuals/aviation/airplane_handbook/05_afh_ch4.pdf.  As far as the throttle-to-thrust mapping, of course, that's going to vary widely by airplane and flight condition.

I understand the energy management system handles Total Energy (throttle) and Energy Balance (pitch). However, I can't rely on reference height(also because it keeps changing ) as it doesn't account for terrain altitude. Is there a way to implement the energy management system without considering height, despite its importance?

If I understand your question and comments, you want a way to get to throttle setting for an air vehicle in prescribed dive conditions (angle, called gamma, and true airspeed). Inherently assumed is zero wind and a trimmed, unaccelerated dive, small angle-of-attack, wings level and no sideslip. Then thrust required will be drag plus weight times the sine of the dive angle:
Tr = D + W*sin(gamma)
Remember, gamma is defined negative for a dive. Of course, drag is a function of airspeed and proportional to its square.

suppose, I can't use any aerodynamic entities here, since I'm using a simulation and don't have the values of Drag and wight. I have limited accessibility - i.e pitch and airspeed, TECS was something I implemented, however i'm unable to control my airspeed through it @AeroAndy

You are on the right track: speed is controlled by pitch.
But it is crucial to understand power (throttle) determines whether one climbs, descends, or flies level for a given pitch setting.

pitch controls airspeed, power controls altitude.

No power at all and the aircraft simply glides at the airspeed of the pitch setting.  It's (straight line) path is below the horizon.

Gravity is the other factor that can contribute to forward propulsion.

This is how a glider maintains airspeed.  Mathematicly, the propulsive force is sine glide angle (to the horizon) × aircraft weight.
To fly with no loss of altitude, add power.  To climb, add more. Now thrust is opposed by drag and sine climb angle × aircraft weight.

I simulated different conditions to observe how the aircraft will fly at different pitch angles.
however I have no information for the weight or drag of the aircraft- since its in simulation (i'm assuming weight as per a model and drag negligible )
I will observe the changes once I implement a propulsive force for the FW in simulation- could you clarify what is he glide angle here ?

@developer well, that's what weight and drag are all about.  Most of us do well to understand gliding first.  Propulsive force = drag at the velocity adequate lift is produced.  Propulsive force = sin glide angle × weight.  It is important to determine Velocity Best Glide.  That's where glide angle (below the horizon) is least.

here's what I'm trying to achieve
let's assume we have a maximum dive angle , now corresponding to this I want to be able to command an airspeed  to descent at a constant air speed i.e (T-D<0)
instead of hit and trial to find a throttle percentage to match the dive angle and airspeed. I'm trying to control the throttle as per these conditions. In a simulated world where I let ardupilot give an throttle percentage based on a maximum pitch, this airspeed overshoots

I also don't think I can visualize drag here, any suggestions for a better flight simulator (I'm using ardupilot with qcgs)

@developer drag will increase from a Vbg minimum both faster and slower.  Your maximum glide angle will be based on Vne, or perhaps a bit slower for safety.  Using sin glide angle × mass will give exact propulsive force for any glide speed in a linear steady state.  Then propulsive force = drag.  Note glide angle is also steeper slower than Vbg.  This is why Vbg gives maximum gliding distance.


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Is there a place to land a private plane in or near Virginia City NV?
Is there a place to land  a private plane in or near Virginia City NV?

https://skyvector.com/ is kinda a "Google Maps" for airports and routes.
This Map shows Virginia City is roughly equidistant between Dayton Valley Airpark, Carson City and Reno/Tahoe International

Typing "airfield locator" in Google pointed me to https://www.airnav.com/airports/search.html or https://landingfinder.com (but there are probably dozens if not hundreds of alternatives) which in turn both pointed me to Dayton Valley Airpark, 7 miles away (and a number of other alternatives).


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Why are yaw rate and pitch rate obtained by these equations?
I am reading "Introduction to Aircraft Aeroelasticity and Loads" by Jan R. Wright and Jonathan E. Cooper.
The book said: In steady bank turn (as shown in picture below), The rate of turn is given by:
$\omega_{turn} = V/r $  (I understand this)

And so the aircraft experiences steady yaw and pitch rates given
by':
$n_{yaw}= \omega_{turn}cos \phi$
$q = \omega_{turn}sin \phi$
I don't understand 2 equations above. I think the yaw rate would be equal to the turn rate and the pitch rate is zero.

The yaw rate and pitch rate are in the frame of the airplane, not in the frame of the earth. If the pitch rate is zero, then the plane will fly a inclined circular path (one side of the circle is higher) when viewed on earth.

Turn rate is referenced to earth axes, yaw rate to aircraft axes, hence the $cos\Phi$:

If you turn at $\Phi$ = 0, your rate of turn is the yaw rate and the pitch rate is zero.
If you turn at $\Phi$ = 90°, your yaw rate is zero and your pitch rate = rate of turn.

In order to maintain a steady turn and not lose altitude the pilot does need to pull on the stick when turning..

The pilot needs to pull for two reasons: 1. Trim for higher lift, 2. Compensate pitch damping.

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Does turbulent flow have boundary layer ? Does separated flow have boundary layer?
I have a little confusion between turbulent flow and separated flow. Consider a flow over a typical airfoil: Does turbulent flow region have boundary layer ? Does separated flow region have boundary layer ?

The boundary layer is the volume between null airspeed surface and ambient airspeed surface. The null airspeed at some point stops being bound to the wing surface, at the surface the flow is reversed. The boundary layer still follows the null airspeed surface (source). So the boundary layer looks a bit like this (there is a mistake in the exact location, but this is the idea)

Yes.
There are boundary layers (BL) in laminar flow, turbulent flow, and the
transition between the two.
"Flow separation occurs when the boundary layer travels far enough against an
adverse pressure gradient that the speed of the boundary layer relative to the
object falls almost to zero. The fluid flow becomes detached from the surface of
the object, and instead takes the forms of eddies and vortices."
From: "Flow Separation"
https://en.wikipedia.org/wiki/Flow_separation
Note that the shear stress at the wing surface drops to zero (or very close to zero) after the BL separates.
It is also possible for BL to re-attach to the wing surface after an initial separation. In that case the shear stress returns to a non-zero value.

what are the values of shear stresses at the wing surface in the flow separation region ? Do they have values that opposite the drag !?

Most often in models I have seen, the shear stress is assumed to be zero, or very close to zero at the wing surface after separation.

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Why are some dynamic derivatives not included in DATCOM file?
I am trying to understand Flight dynamics, particularly I am using Missile Datcom to get aerodynamic parameters of a missile, then use MATLAB, simulink to simulate its trajectory. It seems there are a lot of dynamic derivatives, have a look at
this, look at some dynamics derivatives.
 So why don't we have Normal-force derivatives due to yaw rate or Normal-force derivatives due to roll rate ? why don't we have Yawing-moment derivatives due to pitch rate ? etc...

It depends on the File Type you look at. File Type 42 (the most recent) has more dynamic derivatives. (If I understood correctly your question)

@Afe, I mean which dynamic derivatives do we need in order to simulate a flight of an aircraft? I see Cn, Ca, Cy, Cm, Cl,...(6 coefficients) and pitch rate, roll rate, yaw rate, rate of angle of attack, rate of side slip angle (5 rates) so we could have 6x5 = 30 dynamic derivatives. Why don't we have other dynamic derivatives like: yawing-moment derivatives due to rate of angle of attack?

Why was this question voted to be off-topic? It's perfectly legitimate question to ask about flight dynamics...

A plane is subject to 5 forces: Thrust, Lift, Drag, Weight/gravity (and side force). In addition, there are 3 moments: Rolling, Yawing and Pitching moment. With these 7 vectors you are able to represent how a plane behaves in the air. The problem of simulations is how to compute these 7 vectors for a complex shape like is an aicraft in different flight conditions. To obviate these issues, engineers came up with 'coefficient of ..' which is indicated by C_letter.
To make estimation of these coefficients more accurate, engineers decided to compute the partial derivative of each coefficient due to 'something'. However, some of these derivatives have a small influence on the coefficient such that only for high fidelity simulations they are used (for example in Level-D simulators). Moreover, depending on the type of aircraft, some derivatives may be important or not: if a plane has no slats then there is no lift coefficient due to slat failures.
DATCOM was developed in the seventies and computing power has improved a lot since then, therefore some coefficients are not included (yawing moment due to angle of attack).
A nice reference to understand why coefficients are used if the book Boeing - Jet Transport Performance Methods.

could you help me out, looking at https://www.mathworks.com/help/aeroblks/digitaldatcomforcesandmoments.html
It seems like: $C_{L \space  total} = C_{L \space static} + C_{L \space dyn} = C_L + (C_{Lq}q + C_{L\dot \alpha}\dot \alpha)(c_{bar}/2V)$. I understand static coefficient derivation, where do dynamic derivative contribution formulas come from ?


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How to calculate the drag on an airfoil from momentum equation (Fundamental of Aerodynamics 5th edition, J.D.Anderson)?
If you got the book, please read 2.6 section (page 135). Here is my sumary of this section:
An airfoil in a wind tunnel (wingtips were butted against both sidewalls of wind tunnel). The control volume is 'abcdefghia', it has unit depth in the z direction (perpendicular to the page). Through some steps that you can read from pages, we got:
$$ Drag\space on \space the \space airfoil =  -\unicode{x222F}_{ai+bh}(\rho \vec V.\vec {ds})u $$

In experinment, how can we know where the line bh is, how long it is..?
In the picture above, can we move line bh backward (to the right) ?
How big is the wind tunnel or how far from top to bottom walls of the wind tunnels (with given airfoil)is in oder to have the lines ab and hi ?
Do you feel this method is very inaccurate with a lot of negligibly and pitot rake thing (page 141) ?

@Peter:
Thank you, nice to hear that !! . Actually, I thought I understood this section until I face the problem 2.2 at page 198 (by the end of chapter 2). I reviewed this section and a lot of questions arised. First, sorry because English is not my mother language.
1st question: I really have no idea where the line bh is (both in vertically and horizontally) and how is the length of bh ?.
2nd question: Suppose we already have the line bh located properly. My physical feel tell me that the line bh can move backward and the velocity gradinent $ u_2 $ = f(y) stay the same. But imagine in real life, if we move the line bh far enough, the velocity gradient $u_2$ will be uniform and equal the freestream velocity $u_1$ !!
About the third question, I think: we must have top and bottom walls of the wind tunnel that the pressure over them is equal to the free stream pressure, I mean: move them far from the airfoil in vertical direction so that the pressure over them is uniform and equal to freestream pressure.
4th question: I still had no idea because I never use my hands to do these kind of experiments, but my instinct tell me it will have a lot of errors.
My word maybe too dumb but I'd like to learn what people do in real experiment.

I'd be interested to hear what your motivations are for these four questions and what you've done yourself to answer them.

Just inform you, I have answered your question by editing my question

You are basically asking two questions here:

How do we choose an appropriate control volume?
What effects does the physical geometry of a wind tunnel have on our ability to make accurate measurements?

Contol-volume selection
Young, et al., have some nice words:

Any volume in space can be considered as a control volume. The ease of solving a given fluid mechanics problem is often very dependent upon the choice of the control volume used. Only by practice can we develop skill at selecting the "best" control volume. None are "wrong," but some are "much better" than others.

The researchers who came up with the control volume in your image had plenty of practice and knew how to cleverly decrease their computational load through control-volume selection. They could have selected a control volume outside the wind tunnel—or even 1000 miles from it—but this approach would have required a lot more work to obtain their results. I suggest looking through this set of notes for a mathematically inclined presentation on the control-volume selection in this particular case (it will also help you with problem 2.2 and your second question). Alv's answer discusses some of the more qualitative factors influencing the control-volume selection in this instance.
So to answer your first two questions specifically, you can put $bh$ wherever you want and make it as long as you want, but there is an advantage to setting up the control volume the way it is in your image.
Wind-tunnel experiments
To answer your third question, the walls of the wind tunnel would ideally be infinitely far away from the test article. Such an arrangement is obviously impossible, so various wall-interference corrections are developed. Here is a brief overview of those corrections; a simple Google search will yield much more information. Individual tunnels will develop their own set of corrections that include things such as the appropriate size for a model and the distance it should be from the walls (also search blockage ratio).
Wind-tunnel design can also help mitigate wall interference. Many higher-speed tunnels feature slotted walls in their test sections to strike a compromise between directing the flow of air and allowing pressure disturbances to dissapate.
Specifically to your fourth question, the accuracy of your results will be determined by how judiciously you determine and apply your corrections. Given that wind tunnels are still used in industry to develop new airplanes, we can be certain that there is a way to get reasonable results. Even further, the data produced by the very studies Anderson describes is still used by engineers and scientists; the pressure-integration method has proven quite robust over the years.

those are some great questions. I will try to be very concise.
Firstly, regarding to the line ‘bh’, there is no fixed length you can calculate. Ideally you want to make sure you get measurements of the entire region where there is a momentum loss. Therefore, you seek to take measurements until you reach a point far enough so $u_1=u_2$.
Note that this momentum loss is directly related to the size of the wake, thus the length of ‘bh’ would be determined by the Reynolds number, separation point, incidence, etc. One common problem, especially at high AoA, is that the rake is so large that the wake rake does not cover this ‘bh’ line. This would mean that the momentum loss measured, and therefore the drag, is smaller than it is physically.
With regards to the distance from the trailing edge: You must avoid being too close since phenomena like recirculation bubbles or the pressure difference between the upper and lower part of the aerofoil would basically ruin your measurements (the velocity is not normal to the probes , etc). On the other hand, the flow in the rake induces an additional momentum loss, thus if you take the measurements farther aft, you would be also measuring this contribution, apart from the drag of the aerofoil. In addition, the size of the wake increases, leading to the problems mentioned in the first question. Typically, a distance of approximately one chord is used for the experiments.
The next question is related to a different topic, wind tunnel corrections. From the picture, due to the momentum loss, using the equation of continuity, you will always have $ai<bh$. What is defined as ‘”streamlines far away from the body”, lines ab and hi, are assuming constant pressure and velocity. If you add the wind tunnel boundaries, imposing the streamlines to be parallel to the surface of the tunnel, there would be an acceleration of the flow, $u_1<u_2$, thus this p=p_infinity will no longer be achieved.
This change in the velocity profile will affect the measurements at the rake, therefore some corrections are needed. The bigger the wind tunnel is, the smaller the corrections are. In the book you will find a nice chapter about this.
Regarding to the last question, unfortunately I don’t have the book anymore… But this method has indeed some drawbacks (in addition to the ones aforementioned). Firstly, the pressure drag is almost neglected. Moreover, measuring the turbulent flow at the wake is difficult and leads to errors  if the velocity is not normal to the probe (this happens especially at high AoA).
Hope this has helped!


text:
How do I calculate the normal component of the velocity at the midpoint of a source straight panel?
I am reading "Fundamental of Aerodynamics " by J.D.Anderson Fifth edition. Now I am at the chapter 3. If you got the book, please go to the page 286, the part that says: "when j = i, the contribution to the derivative is simply $\lambda/2$ ". How could it be $\lambda/2$ ? I thought it would be zero.
I will summarize the problem for those who don't have the book:
We have a uniform flow and a source sheet cover the the surface of a known body. We have to find out the $\lambda=\lambda(s)$ along the source sheet that when we superimpose the uniform flow with this source sheet, we obtain the streamline over surface of the body.

A source sheet is an infinite number of line sources side by side,
where the strength of each line source is infinitesimally small

We approximate the source sheet by a series of straight panel over the body surface (if we take n panels, then we have to find n values of $\lambda$)  and calculate the velocity at each panel and set the normal component of it equal zero.

Take a point $P$ at the middle of $i$th panel and calculate the velocity at $P$ induced by the panels, or just calculate the normal component of the velocity at P. The book said that the normal component of the velocity contributed by only $i$th panel at the mid point $P$ of this panel is $\lambda_i/2$. I don't know how to calculate this, I have tried and thought it would be zero.

@Peter: Look at the image, you can see the velocity induced at P by the panel i is in the ab-line direction (I mean the horizontal direction). Then, the normal component (vertical direction) of it will be zero

Perhaps you could share how you tried and obtained zero?

A source panel will only produce flow normal to the panel. The horizontal component is zero, not the vertical.

normal at every point ?? I agree with this but it's only true for some point. At the control point or the midpoint of the panel, due to the symmetric, the velocity is zero

Yes, at every point. We define the normal component of the overall flow (freestream plus all panels) to be zero only at the control points, but you're specifically asking about one panel's contribution to itself. We only need to worry about the flow from the panel in question, which is always normal to it.

You can find a mathematical derivation of the $\lambda_i/2$ result in Katz and Plotkin, chapter 10. In this PDF, the result you are looking for is on page 234 (250 of the file itself). Anderson approaches things a bit differently, but you should be able to see at a high level how the approaches are analogous. The math gets a bit complicated and it's really not necessary to comprehend every step in detail to understand the application to aerodynamics. However, a good exercise if you really want to dive into the math is to translate Katz and Plotkin's approach into Anderson's notation, or vice versa. For me, though, it's good enough to see that it can be done and move on with the more interesting applications.

Thank you for the PDF file, I understand the $ \lambda / 2 $ result. I still do not agree with you that the source panel produces only normal velocity at every point (yes, the flow is produced by only one straight panel). In the PDF file, on page 250, equation (10.20) is the horizontal component of the velocity at P, it may not be zero at every point. It only equals zero when 2x = x1 + x2, or P is on the mid line of the panel.


text:
What is the meaning of the term "fly back only" in AMM documents?
I am reading an AMM document and I don't get the ideas below:

Examine cracks in area A1 and A3:
(a) Accept with an inspection each 100 hours, cracks on the inner or
  outer shroud if there is:
A single hair line crack at the leading edge of the blade, possibly only on the coating on all blades (Area A1).
(b) Accept for fly back only, cracks on the outer shrouds if they
  are:
A maximum of 0.08 in. (2.03 mm) long on up to 10 blades (Area A1).

I don't get the whole idea of the sentence (a): why is that: the cracks are on the shrouds then they turn to be on the leading edge of the blade ?
And what is the meaning of the term "fly back only" in the sentence (b) ?

More concerning would be the use of "accept" instead of "except". It probably means it is ok to fly the aircraft back to a maintenance facility.

@RonBeyer -- I think "accept" is the correct usage here given the stuff in (a)

(a) Accept with an inspection each 100 hours, cracks on the inner or outer shroud if there is:
A single hair line crack at the leading edge of the blade, possibly only on the coating on all blades (Area A1).

The statement translated means; Allow to continue in service with 100 hour inspection cycles the following defects.

(b) Accept for fly back only, cracks on the outer shrouds if they are:
A maximum of 0.08 in. (2.03 mm) long on up to 10 blades (Area A1).

Allow for One Time Flight Only, as described in the operators Op Specs and MEL, the following defects


text:
Are any software or aeronautical engineers yet attempting to design pilotless passenger planes (PPP'S)?
With all of the effort currently under way to attempt to create driverless land vehicles (which I believe may be a rather misplaced effort) has anyone yet heard of any serious efforts also being made to one day try to eliminate passenger jet pilots as well?  As a former private pilot myself, such a thought seems rather ludicrous, but just wondering.  It seems to me the elimination of humans from overseeing human safety concerns such as flying or driving, would simply be "unsafe."

Serious is relative and open to interpretation.

There are cases where automation is simply safer than human, and autonomous cars are possibly a good example. Experimentation is in progress, and under a strict legal framework. I wouldn't be surprised the ratio of accidents is already better than for the average (and tired) driver. just an opinion. The number of accidents in aviation has decreased with fly-by-wire and FMS.

In many cases, autopilots tend to outperform humans when it comes to precision and attention... when they work as they should. Automation tends to be ineffective to adapt to unexpected/unforeseen circumstances. Especially when it comes to conflicting sensors. The ratio of accidents caused by human vs automation is well in favour of automation. But there are no statistics being kept (unfair) how many times the human on board prevented the automation from a fatal crash. I've personally had to intervene twice with one of the most advanced autopilots in the business.

Yes, standard auto-pilot, when used on long duration flights at straight and level, actually enhances safety.  But to then actually try to eliminate all actual onboard human oversight, whether or not this has yet been proven to enhance safety, is what I was trying to get at here.

Personally, it is my best guess that should anyone ever try to force "driverless semi trucks" on the rest of the driving population, before they might first have been proven to be reliably, clearly, and undeniably safer than the human-driven ones, would be "suicidal" for the "driverless movement" amongst technologists.  I personally suspect that such "proof" is still most likely several decades away, and not mere years away.  With aircraft, my guess is we may be looking at "generations" away and not years.  Sorry for the "opinion."

Serious discussion of removing passenger jet pilots?  No.
Serious discussion of making pilotless VTOL aircraft? Yes.
Uber, for one, is already working on this. Check out this quote from page 40:

To fast-forward to the safest possible operational state for VTOL
  vehicles, network operators will be interested in the path that
  realizes full autonomy as quickly as possible.

Uber, Airbus (x3), Lilium, ...

A pilotless aircraft would be like an army where the commanding officers stay home to command remotely.  Not only an act of cowardice, but also not good for the army's actual quality of command, as it seems to me that "armchair quarterbacks" whether robotic or not, will never take the place of real quarterbacks, nor should they.  Having the "general" near the front lines has always impoved the safety of the troops, and the effectiveness of the army.  So having responsible human operators of vehicles where human safetynis at possible risk, will always improve the safetynof the humans.

If you ask me, anyone who would attempt to remove a responsible human operator from an aircraft, by definition is creating unnecessary safety risks for the human passengers left behind without any human pilot to watch over them and to necessarily risk his or her own life at the same time in the process of assuming such a responsibility, in the course of their occupation.  Sure, where ever human safety is not affected in any way, automate, but where human safety is affected, direct onboard human oversight should be retained.

Hi @ScottFrancisPerry, welcome to Aviation.SE. We like to talk about only one thing at a time around here. Your comments seem to be about whether there should be pilotless aircraft, while your original question (and my answer) are about whether anyone is considering pilotless aircraft.

In my personal opinion, there are several reasons why pilotless commercial passenger jets won't or at least shouldn't happen anytime soon.

You can only program a computer to handle an x number of situations. Better computers can perhaps handle some unexpected situations, but not as well as humans can. Then of course there are going to be unknown bugs in the software/hardware. So someone needs to be able to take control if the computer no longer can handle the situation. If this person is on the ground, this must be done through a network connection (be it through the internet or otherwise). If that person is able to do it, another organisation will be able to crack it. If they cannot secure the NASA and/or the Pentagon well enough, they can't secure an airliner sufficiently. Therefore I believe there should always be at least one person on board who can take control
The fairly recent Germanwings crash where the copilot locked out the captain and crashed the aircraft to kill himself and get his name in the books by killing all people on board shows that if there is one pilot in the cockpit of such jets, there should always be a second pilot.


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Under what conditions does the FWC give the PITCH PITCH aural call-out on the A320?
I wanted to find more detailed information about the PITCH PITCH aural call-out that the FWC gives out on the A320. However it is not listed in the FCOM. It would help alot to understand about this feature.
It would be really helpful for an official reference also.

The "PITCH, PITCH" synthetic voice is called out when

"The aircraft pitch attitude is becoming excessive during flare an
  landing."

This is an optional feature which airlines can install to avoid tail strike.
Source: ECAM Description, Indicating/Recording Systems, Aircraft Systems, A320 FCOM

I have read this but I wanted to find out more detailed information how the system works. I have modified the question accordingly. Thank you

@Jai there is no mention of how the system is implemented. However, under the "Normal Procedures" chapter, it mentions the Pilot Monitoring should announce "PITCH PITCH" if the pitch attitude approaches the tail strike pitch limit indicator, or reaches 7.5°. It is therefore reasonable to assume the automated callout is a digital implementation of the above.

“PITCH,PITCH” is called out on excessive pitch attitude durring flare or excessive pitch rate (ie. FWC estimates that pitch att WILL be exceeded shortly).
This can cause an occasional spurious trigger when the pilot is a bit late&abrupt in his flare and triggers quick nose up defletion, even though he is arresting that pitch-up before it gets dangerous for a tail-strike (eg say 6deg), you might still get this warning, based on the pitch rate alone.
What is the exact pitch angle and pitch rate that will trigger this alert is anyone’s guess, as it is not present in any documentation that I have found. Suffice to say that a properly executed approach and flare will not trigger it, regardless of weather conditions. In my experience, only poor execution by the pilot will.


text:
Why do the old A320s have a lower tailwind limitation compared to the newer enhanced ones?
In my company on the older A320s particularly the ones which are in the MSN 2000 range their tailwind limitation for takeoff and landing is 10 knots. But our newer enhanced ones have a 15 knots limitation. Any reason for this? Does Airbus do any modifications to the aircraft so that it's tailwind limit increases?

I believe it may be customer specific. In my old company, it seemed possible to purchase increased tailwind limits from the OEM for some aircraft types. Not sure whether that is the case for old A320s, though.

At least three possible reasons come to mind, a) more powerful engines, b) better breaking - perhaps improved carbon brakes. c) better electronics  to handle rejected takeoffs. Also improved mechanisms such as speed brakes or lift dumpers. - this is just a guess that perhaps will help someone else in their research :)

@jwzumwalt  Do you mean "braking"?


text:
Why is there an altitude limit if we have an IDG failure on the A320?
In my company’s MEL there is an altitude restriction if we have an IDG failure of 33500 feet why is that?

Short answer: This is the highest altitude where the APU can deliver 90 kVA at ISA temperature.

Details
In normal conditions, electrical power is delivered by two engine integrated drive generators (IDG), one per engine.

IDG used both on a IAE V2500 and CFM56-5B engines. source
Each IDG is able to deliver 90 kVA, a power which is sufficient to feed all systems in the aircraft. As electrical power is vital, a second source is provided and each source feeds half of the systems, but is ready to take over and feed all systems in case of failure of the counterpart.
When one IDG is off, the auxiliary power unit (APU) is used as a backup for the second source. The APU delivers both hydraulic power and electrical power.

Honeywell 131-9A APU. Source
At ISA temperature and below 33,500 ft, the APU electrical generator has the same 90 kVA generation capability.

Source: FCOM (3.1.49)
After 33,500 the APU efficiency for electric power generation starts decreasing. If the aircraft was above 33,500 ft and the second IDG failed, this would leave the plane with a single generator (the APU) unable to deliver 90 kVA required by all the systems. So the altitude limit in the SOP.


text:
What are the reasons behind switching FDs off for a VOR approach?
Why do SOPs ask to switch off flight directors and enter Vapp into the FMGC while carrying out a VOR approach on Airbus aircraft? My question pertains to when we disengage the AP. Why do we carry out these actions?

If we leave it on what effect will it have ?

Okay I still quite don't get it ? Doesn't the V/DEV function help us manage our V/S? We are correcting our pitch angle there to and as a result thrust will change. My question pertains to when we disengage the AP.

problem is you shoudln't really use the V/DEV as your primary/single guidance durring approach. DME vs. baro altitude is a good crosscheck that will give you the correct FPA to stay on descent profile. Converting FPA to VS is a bit too math intensive though...

ok two questios there really:

entering vapp as speed constraint at the FAF.
After the FAF you want to be flying a constant 3deg path (or whatever the approach gs is). Changing configurations and deploying flaps while on final will make the aeroplane baloon and deviate from that flightpath. To minimize those (uncorectable) deviations, the SOPs will call for the aircraft to be fully configured (flaps full, gear down and Vapp) at the FAF when starting the final descent.
By entering the vapp in fmgc at the faf you are basically telling the computers I want to slow down early and configure to full flaps before thr FAF. The fmgc will then compute your descent to allow for that deceleration segment. It's not SOP as far as I can tell, just a gimmick people use to tell computer you want early stabilized.

Switching FDs off
Two points here: you are not switching them off at the FAF. You are changing them to a TRK/FPA mode (usually 1nm from FAF) to better control your glidepath angle durring final. Yes, you could use v/s to do that, and use trigonometry to compute the v/s required to maintain 3 deg for a given groundspeed, but why would you.  Changing winds will change your groundspeed, and thermals will mess up your flight path. Setting -3deg in the FCU is much easier.  I can then set -3.2deg if I get, say 20 feet high, and I should be back on profile in about 1nm.
Second point: FDs will be switched off (completely) after disconecting A/P and at least at reaching minimas. Reason is the ap guidance is not certified to guide you after that so it is manual/visual flying using PAPI if available.

Note: this is all about flying a manually-selected non-precision approach (eg in NAV/FPA or TRK/FPA) mode with AP on. Using a fully managed approach is a different story

Great that clears it up a lot. Where is it mentioned that the AP is not certified to guide the aircraft beyond minima? In case someone asks

FCOM-NOR-SOP 18 says Disconnect AP  "At the latest at the MAP or Minimum Use Height of the AP (whichever occurs first)" . Minimum AP height for non precison is 250ft (FCOM-LIM-AFS-10). At the MAP the FD will revert to HDG/VS if not disconnected , so you really don't want to keep AP on beyond that...


text:
How will the alpha lock function intervene when performing a takeoff at heavy weights on the A320?
In the FCTM for the A320 family of aircraft's under the SOP Takeoff chapter it is mentioned that the alpha lock function can intervene when performing a takeoff at heavy weights.
Can someone please explain the logic behind this ?

Alpha Lock is a protection that will prevent surfaces retraction after take off if the angle of attack (ALPHA)is high for the next retracted position of the flaps/slats lever. So even if the pilot puts the selector in the retraction direction the order will be postponed till the angle of attack decreases. This is managed by the Fly By Wire logics. The logics takes into account more particularly the angle of attack and the configuration speed limits.

On A320, it can only happen between FLAPS 1 and FLAPS 0 conf. And only if AOA Is over 8.5deg or speed below 148kts.


text:
How does CONFIG FULL provide better handling capabilities in turbulent conditions?
I wanted to get some clarity as to how does CONFIG FULL provide better handling capabilities in turbulent conditions?
This line mentioned in the A320 FCTM under the the supplementary procedures chapter
PR-NP-SP-10-10-3 P 3/4. But there is no explanation to it.
Could anyone help clarify. From what i can deduce this is from an aerodynamic aspect

I am not sure but CONFIG FULL reduces the stall speed and increases the lift which means that the aircraft can cope more easily with changes of wind speed/direction

Can you share the exact sentence in FCTM? I can't find it in my FCOM copy

@ocirocir that's because it isn't in the FCOM its in the FCTM. Kindly read the description of the question I have mentioned the exact reference.

@Jai Sorry I misspelled the last word, I mean that I can't find it in my FCTM copy.

@ocirocir the exact reference is attached in my question post. What's so difficult in finding it ? I presume you are aware of how to navigate to the specific chapter using the reference I have given.

@Jai There is nothing related to CONFIG FULL in my FCTM at that section, that's the point... You know there are different versions of FCTM, so providing a screenshot or copy and paste that line would be helpful to help you...

It's almost a certainty that this is not the case. Airplanes have better handling capability at lower flaps settings- why? because you're flying faster and therefore ailerons and rudders are more effective. But then again this is an Airbus.

@dashman that's the exact same thought which came to my mind when I read this line and it caused quite a bit of confusion.


text:
Where can I get full audio cockpit recordings of all four flights involved in the 9/11 attacks?
First of all, this is a question specifically asking about the September 11th, 2001 attacks. It is not focused on NTSB or other accident investigations in other countries. If you think it is, please explain your reason.
I have always been curious to know how people reacted to that terrible day, and if I remember correctly, there was a thirty-one-minute recording from flight 93 that started with someone saying there was a bomb on board up until the crash.
I guess the main reason I am so focused on sound is because of something I am going to explain to you all. I am a totally-blind user who uses screen reader technology and accessible web sites to brows. Since I cannot obtain visual information and expressions, my next source of information is how things sound. It is frustrating to not have this information. Someone could tell you that this or that happened, and it looked horrific, but if you can't see it, how do you know? Maybe some people would say that it was a blessing that you didn't have to see such things, but still, I feel like I'm missing out on something. Sounds of horror, of grief, all of those can be just as traumatising to hear as one would see an image. I have spent numerous hours on YouTube, trying to find stuff to add to my audio memorabilia of 9/11, because as we move through history, I want people of the future to know how everything played out from beginning to end, what people endured, how many people were killed, hurt, and willing to risk their lives to help rid the bad guys. Most importantly, I want them to experience all of this without the ability to see what's going on. If you can hear the recordings, you should be able to make pictures based on all of your senses, and you'll be able to make appropriate emotional responses.
Also, a friend of mine inspired me to do all of this because she had a former acquaintance of hers, who is no longer her friend tell her that 9/11 never happened, that it was all a conspiracy. So I vowed to help her out by obtaining as much proof as I could by making a file containing as many audio recordings detailing the events of that day.
I have heard that the NTSB is exempt from releasing these audio recordings even with the FOIA, but I believe that if you can approach an attorney, you can circumvent this exemption by claiming that such recordings must be available for historic reasons. I don't know if they will release it twenty-five years later, fifty years, seventy-five, or a hundred years from now.
And yes, there has been evidence of CVR recordings being leaked into the public, which is like finding a rare piece of jewellery since they are scarce.

Most likely what you have heard is not the CVR recordings, but recordings of several telephone calls made from the aircraft. One of the flight attendants on AA flight 11 made an Airphone call to American Airlines operations. There were also a few calls made on cell phones from flight 93. These recordings are available but not the CVR

Your question has been answered: it would be illegal to release CVR audio. End of story. FOIA and "historical significance"  and all else don't trump the explicit Federal law. True, that law has, in very rare occasions, been violated in the past, but the audio from 911 remains secure. Which is as it should be.

Additional stumbling block: for two of the planes (AA11, UA175), the CVRs were never recovered (neither were those planes' FDRs, for that matter), and were presumably destroyed by impact forces and/or the intense, prolonged postcrash fire, while for a third (AA77), the CVR was recovered, but the recorder had been broken open by impact forces and the recording medium destroyed by fire (see for yourself), meaning that obtaining audio recordings from those three CVRs would be literally impossible even if it were legal to do so.

The short answer: you can't. Federal law prohibits the release of CVR audio, though transcribed excerpts (if they are relevant to the investigation) are made publicly available once the accident report is released.
See 49 USC 1114(c):

Cockpit Recordings and Transcripts.—(1) The Board may not disclose
  publicly any part of a cockpit voice or video recorder recording or
  transcript of oral communications by and between flight crew members
  and ground stations related to an accident or incident investigated by
  the Board. However, the Board shall make public any part of a
  transcript or any written depiction of visual information the Board
  decides is relevant to the accident or incident— (A) if the Board
  holds a public hearing on the accident or incident, at the time of the
  hearing; or (B) if the Board does not hold a public hearing, at the
  time a majority of the other factual reports on the accident or
  incident are placed in the public docket.


text:
How does this Bell 206 cyclic control linkage work?
I'm studying the Bell 206 Maintenance manual to understand how the pilot's control inputs get converted to swash plate movements.
This diagram seems to explain the cyclic well, but I can not figure out how the lateral stick movement is transformed.

Here is an example of how the crank mixer is operated by the cyclic (Y bar 9)
The forward-aft movement of 12 (the stick) causes member 10 to rock back and forth, moving 9 back and forth, which operates the mixing cranks at the end (connected to 7 and 8).
However, it looks like the stick can't mover laterally at all, since 10 can't move laterally (?) I can't figure out even why 10 has a provision for motion in the vertical plane in the first place.
Perhaps I'm misunderstanding how 12 moves? I'm assuming it pivots around the base (15).
A more detailed view of the linkage:

Thanks!

Does this answer your question? How do a helicopter's cyclic and collective transfer commands to the swash plate?

I have read those answers thoroughly. I understand the principle. I wish to know how this particular design works. There is something about the lateral motion of the stick here I do not understand, since the linkage 10 looks like it will lock any lateral motion.

You should provide a link to your source, both for attribution and so people can see any related material. Different views sometimes clarify operation.

@Pilothead done, thanks.

That's good, and your second illustration shows the spherical bearings at 5 and 16.

9 is a rigid structure held in a single plane by three links, two forward (one is the cyclic) plus one at the rear. It replicates the cyclic position in the rear link (and incidentally in the other forward link) and cannot by itself cause a differential motion in 7 and 8, which is the rear link's job.
The picture is insufficiently detailed. The links (view C) at the ends of 10 use spherical bearings to allow lateral motion. 10 does not move vertically, it moves laterally which moves 9 laterally which imparts a tilt to the poorly illustrated link at the back of 9 which moves 7 and 8 differentially. An axial twist in 10 is the same motion as 10 and 9 fore and aft, and is the means by which that occurs. The pivots are the bottom spherical bearing in view C and similar attached to cyclic.
From ebay

@jim An axial twist in 10 is exactly the same motion as 10 and 9 fore and aft, and is the means by which that occurs. The pivots are the bottom spherical bearing in view C and similar attached to cyclic. 9 is a rigid structure held in a single plane by three links, the two forward already mentioned plus one at the rear. It replicates the cyclic position in the rear link and cannot by itself cause a differential motion in 7 and 8, which is the rear link's job.

Ok. That’s an interesting linkage, but I think I’ve got it now.  Thanks.

Very nice explanation - thank you for finding that picture of the linkage. I understand now!


text:
Is there an ATC radio backup?
I was thinking, what would happen if the radio systems for an ATC tower fail due to power loss or faulty systems?
Is there any kind of backup radio that would be used to contact the planes and/or any procedures that the planes and ATC would follow?
Edit: And if there is a backup radio, what happens if that fails too?

I think the last time a total ATC failure happened at an airport was 2011, Sendai Airport during the Tsunami. By the time the radio and radar went out it was patently obvious that having your plane on the ground there was not anyone's idea of a good time. Other ATC was managing diversions.  Like the answers below state, it's really only a total-catastrophe situation that can completely knock out radar and radio. Short of major physical destruction the backups can deal with almost anything. And if the site has suffered such massive damage then there are bigger problems to worry about.

I was doing an IFR training flight and when we asked for a clearance we were told "Columbus is dark." We were flying out of KOSU and talking to controllers there but KCMH was unreachable and apparently all traffic was being worked by Center. I never found out what actually happened but ended up bagging the lesson as the KOSU controllers told us there were only the 2 center controllers working everything. This was within the past two months.

There was an incident in 2014 where an employee of a contractor working at Chicago Center deliberately sabotaged the equipment as part of a suicide attempt, disabling the entire facility.  This wasn't exactly a normal case, though, and it's not clear that any number of backups would have kept the Center running.

There was also an incident at Miami TRACON about a year ago.

There is always a backup radio system as well as a several backup systems like for example a backup CWP (controller worker position) in case the primary fails. PANS-ATM (ICAO doc 4444) in chapter 2.5 SAFETY REVIEWS mentions that

Operational and technical issues to ensure that: [...] communications, navigation, surveillance and other safety significant systems and equipment [...] include adequate backup facilities and/or procedures in the event of a system failure or degradation.

Emphasis is mine.
Also there is a standby generator (or even more than one) that has to instantly take over in case of power supply failure but I can't find any regulations at the moment.
As for the "what happens if the backup fails as well" question, we need to see the fuller picture that the document provides:

d) communications, navigation, surveillance and other safety significant systems and equipment:
1) are tested for normal operations on a routine basis;
2) meet the required level of reliability and availability as defined by the appropriate authority;
3) provide for the timely and appropriate detection and warning of system failures and degradations;
4) include documentation on the consequences of system, subsystem and equipment failures and degradations;
5) include measures to control the probability of failures and degradations; and
6) include adequate backup facilities and/or procedures in the event of a system failure or degradation;

Emphasis is again mine
As you can see backup is the last line of defense. An ATS unit should ensure that equipment is regularly maintained, it's monitored, it's tested and any failures should be prevented if possible and their impact being documented.
If everything else fails, then you use the backup. And again the "include adequate backup" phrase can be translated as "if one thinks that a second backup is needed they should install one". But the previous 5 clauses are there to eliminate that case.

If the power fails, the tower will automatically switch to backup power generated by local diesel generators. If that fails, there are backup handheld radios. If those fail, the tower has a battery powered light gun for transmitting visual signals. So the risk of losing all forms of communication is next to none.
Everything is backed up in ATC. Radios, radar screens, flight strip printers, phone lines and so on. And should the unthinkable happen and the coffee machine fails, there is usually a backup of that as well.

The light gun works for Tower, but not so much for TRACON or Center. The backup handhelds are also not really sufficient in those cases. But, of course, the worst case is ATC services being unavailable for an entire country, such as in an ATC strike.

I assume that the ATC strike is the result of both the primary and backup coffee machines becoming inoperative.

@reirab One should think so! Just a note though, when air traffic controllers strike, ATC facilities do not close down. Unions have agreements with the service providers to always provide a minimum service, such that emergency flights, state flights, military flights and usually even overflights will be handled.


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How to calculate altitude in a flight simulation?
I guess altitude from sea level in the real aircraft is read from barometer, while for the altitude from ground a radar is used. For the purposes of very simple simulation, and assuming aircraft is on ground at certain airport at certain altitude.
The starting variables are then nothing but a throttle position, which over time increases, which translates into speed. And once the aircraft is airborne also the pitch. For this purpose I would not assume any roll, wind or other factors. The aircraft engine has certain torque % and pilot pulls the nose up to achieve certain pitch.
Is it possible to get the altitude simply as the function of pitch and torque % Or to put it differently what are the minimum variables to take into account to come up with an altitude?
UPDATE
Obviously there's something wrong with the question because it resulted in the explosion of complexity, even touching the topic of atmospheric re-entry.
What I want to know is, as a pilot of a simple simulator, standing still on the runway, I can only change two things.

Throttle, and some time later
Pitch

I don't have to do anything else whatsoever in simple sims, I click on + to set the throttle to X, and when the speed is Y, I pull the nose up, and now the altitude keeps on picking up. How do those two changes to those two variables (throttle, pitch) eventually give me the altitude and speed, through a series of equations (that needn't be neither simple nor linear)?

Ska - what are you using to turn torque into thrust? Engine efficiency, drag etc all are needed. There is no simple model for this.

@RoryAlsop Check the comments under Koyovis answer.

You might want to have a look at chapter 5 of Flight Dynamics in Microsoft Flight Simulator on FS Developer. The model is quite complex for your need, but still a simplified approach.

A simpler method with a certain degree of realism is from the power curve, I've updated my answer.

I see that and roughly understand it. I still don't see how that translates to my keyboard +/- (throttle), and keyUp/keyDown for pitch. Because these are the only things I can change. Should I be able to infer that from your answer?

Have added equations. It's still a multi-dimensional thing unfortunately.

What is k and V?

Well you've edited your question but you haven't added the purpose: game, pleasure, academic project? Something else? That would help determine simple

Game. A simple one with 4 keys +/- throttle, +/- pitch. No roll, no yaw, no winds.

@Ska OK I see. To me game + user input (throttle, pitch) - wind - roll - yaw = something similar to the DuckTale DOS game: http://www.hg101.kontek.net/disneynes/ducktales-pc4.png If you try to do something like that, I guess you will have to ask your question to gamedev. The answers there might be simpler and more relevant.

If I understand the edited question, after takeoff you make no further adjustments to any controls but just watch the aircraft climb until it cannot climb any higher. Given suitable control settings at takeoff, the aircraft might level off at some altitude after flying for a few minutes. Is the question, "What altitude is that?" By the way, it sounds like a boring game.

@DavidK For starters yes, that's exactly it. Next I would like to see how further adjustments to throttle and pitch change things once airborne.

@SteliosAdamantidis Not a bad idea at all, I'll ask there also.

You can't directly calculate the altitude of an aircraft from any set of control settings. The altitude is dependent on the history of the aircraft. For example:

Fly level at full power for one minute, and pitch up suddenly. You will be near the ground, having quite some speed.
Climb at full power for a minute. You will be at high altitude, going quite slow.

In both situations, your aircraft is pitched up and at full power, but at very different altitudes. So, what are then the minimum variables needed?
This answer is quite difficult to give. If you're making a professional simulator, thousands. If you're making a platform game, just pitch and power, as well as some way of knowing the history of the aircraft. Usually, this is just a stepped simulation: at each moment in time, determine what your current pitch and power do to the attitude and altitude of the aircraft, and save it for the next time step. Of course, you need some model for relating these variables to actual accelerations of your airplane, and again, this model can be as complicated as you want or need it to be. See Koyovis' answer for more details on such a model.

Not the real sim but also slightly more complex than a platformer. History, as I mentioned in the question is aircraft on ground, then throttle is set to say 70%, then wait, then pitch up. Now how is my altitude changing?

@Ska Again, there's no easy answer. You can only calculate climb rate if you assume steady state: we have pitched up, and waited for the aircraft to settle at a certain speed. Think about driving a car. You press the accelerator to 70%, now what is your speed? You don't know. You can only calculate the final speed. To get the position as a function of time, you need to iteratively see how much the car is accelerating at each moment in time.

@Ska If you don't know how to calculate a trajectory in space as a function of forces, this question may help you along (you will probably want to do Euler integration)

Let's assume it is for a trivial platformer. I can apply throttle, and I can apply the pitch. I also know my weight, engine characteristics and propeller characteristics. Let's also assume that throttle will be applied instantly with no delay. If I apply throttle X and the speed will increase from 0 to X in X amount of time. Then I apply pitch of X and again wait X amount of time. What would my altitude after this X amount of time?

@Ska The movement of an aircraft is described by differential equations. Except for very simple problems, these are solved with numerical integration. There is no way around this, and if you would read up on numerical integration (for example with the Euler method), you will find that this will suit your needs exactly.

@mins Exactly (although the scene has quite a few inaccuracies: Euler's method is numerical as opposed to analytical, not theoretical; there's no such thing as a parabolic orbit, to name a few)

(well, there is a parabolic escape trajectory, but this is supposed to be about reentry; as far as I know, no human has reached Earth's escape velocity).

Since I have created my own (over)simplified simulator I think I have some authority to answer.
Let's start with the basics, your question is quite broad, if you could mention the purpose of the simulator it would help narrowing the scope down.
Furthermore you say you want a simple simulation but you've stressed pitch. Now you have to calculate:

from the pitch the angle of attack,
from the angle of attack deduce the $C_L$ (coefficient of lift)
from that deduce lift and then subtract the weight
then calculate from the excess lift (if any) the du/dt (ie acceleration)
from acceleration get the current vertical speed and finally
calculate the vertical displacement and consequently your new altitude.

Unfortunately that's not in the realm of simple. Of course it depends on how one could define simplicity.
I would strongly suggest you have a look at BADA and total energy model. They have done some of the dirty work but beware: BADA is not for free, it's not even paid. Only Eurocontrol member countries can use it. That leaves you with the mathematics model (which is not bad) but without any data. That means you don't know:

Aircraft engine so you don't know T.
$C_L$ so you can't calculate lift for a particular aircraft
$C_D$ so you can't calculate drag for a particular aircraft
Aircraft weights so you can't calculate W

For the explanations of the symbols I will shamelessly point you to Koyovis' answer
One might argue that 1 and 4 can be found publicly. But then there is $C_L$ and $C_D$. And one thing that I've learned the hard way, is that coefficients cannot be calculated. At least not easily and accurately. Otherwise there wouldn't be any wind tunnels by today. BADA uses predefined $C_L$ and $C_D$ for each aircraft for different configurations. They don't include coefficient calculation in their model. That says a lot to me.
If you embark on that type of calculations then you are way off what you called simplified simulator. If you decide to do it though, again Koyovis' answer has links to useful questions and answers that I don't want to repeat here.
You can find BADA manual here, at least that seems to be publicly available so I guess (and this is a disclaimer, I'm not a lawyer so this isn't legal advise) you can use the mathematical formulas described in there.
The concept is in general that you have 3 variables, thrust, speed and rate of climb or descent. In each iteration of calculations you specify 2 of them, and then you calculate the 3rd from the equations. The equations though make it a bit more tricky than I made it sound.
Good luck with your simulator.

You linked to a BADA 3 document. BADA 4 has more fundamental calculations. I doubt one could easily get access to the necessary data for an actual aircraft type, but for the purpose of an exercise like this perhaps one could get some airfoil polar graphs and ignore the effects of the fuselage and so forth.

@DavidK BADA 4 is not accessible unless you build a real aircraft simulator or something similar and you can convince Eurocontrol that you need 4 and not 3. OP needs nothing of the above. He simply asked the wrong question at the wrong place.

The information about BADA 3 is useful; I just wanted to clarify that the limitations described above don't apply to all of EUROCONTROL's products. (And this is only for the sake of other people who might see this answer; I agree that the chance of getting any BADA 4 data for OP's purpose is practically nil.)

Newton has worked out for us that every movement is the result of a force, or a balance of forces. The minimum requirement is to have a force model of lift - weight - drag - thrust.
Image source
With a fixed wing aircraft, the forces are a function of:

Thrust
Aircraft speed
Aircraft configuration (high lift devices etc.)
Aircraft attitude in 6 Degrees of Freedom: fwd/aft, left/right, up/down, pitch, roll, yaw. Both relative to gravity and to free airstream.
Flight path

Once all the forces are known, work out the equations and direction of motion as a result of the forces, as a function of time.
All in all not a simple model. You would be able to find the force equations and the flight dynamics in open source software such as FlightGear. One has to adhere to the open source license of course, but one could read the source code to understand what the equations are. These are computed every so often per second, and parameters updated for the next clock tick.
Another possibility, a bit more straightforward, is to consider the energy balance of the aircraft. Engine power or thrust setting is what moves the aircraft, and flight starts with thrust as a function of speed. This energy is converted into increase/decrease of kinetic energy, or increase/decrease in potential energy.
You would still have to know weight, attitude relative to free stream etc, but would now compute vertical lift power (weight * climb speed) and horizontal aerodynamic drag power ( a constant * speed$^3$).
More info in

this question which is about excess lift and power for climbing,
this answer on how to compute aerodynamic constants, then flight characteristics per time step
this answer for torque vs thrust for a helicopter rotor.

EDIT
The above is of course a bit complicated due to the many forces acting, and the fluid dynamic nature of the forces. The second method briefly mentioned above is much simpler: use the aircraft performance curve.
Image source

Power required is a curve, determined by aerodynamic factors and weight.
Power available can be modelled as a straight line, for simplicity's sake.
Increase throttle, and power available goes up/down.
The intersection point between Power available and Required is the airspeed at which the aircraft settles in trimmed flight.
Vertical distance between available and required can be used for climb. Airspeed will then reduce.
The right hand side of Power Required, after Minimum Power Airspeed, is roughly proportional to $V^3$. You could only model this bit for simplicity sake.
Climbing will use up power roughly according $P_{climb} = m \cdot g \cdot c$, with c = climbing speed in [m/s], m = mass in [kg]
Aircraft nose-up pitch is a linear function of climbing power available (simplicity!)

You can see that the airspeed will need to be high enough for the aircraft not to stall.
Inputs change all the time (your power setting and stick pitch), resulting in a new Power Available line and climbing power demand. The response to the new requirements is not instantaneous of course, but slowly creeps to the new equilibrium. How fast or slow can be regulated with a software gain factor.
So with $\delta_{throw}$ the throttle deflection, $\delta_{pitch}$ the stick pitch, and $c$ the climb speed:
$$ P_a = k \cdot \delta_{throt} \tag{1}$$
$$ c = \delta_{pitch} \tag{2}$$
$$ P_r = f(m, V^3) + m \cdot g \cdot c \tag{3}$$
On the runway, throttle setting = power = $m \cdot a \cdot V$

Is thrust == torque? I do know the weight. How do I get drag?

No, torque is the force moment you need to rotate the propeller, there's a graph in this answer. You get drag by multiplying a constant times speed$^2$, the constant changes with air density and pitch attitude. There's a sort of an explanation here. For power considerations you would multiply drag * airspeed.

Interesting. So to get the thrust I also need altitude (air density), and to get the altitude I need the thrust :) Isn't this leading to cyclic reference?

Not if you compute the equations iteratively, and use the data of the previous timestep to compute the data in the new tilmestep. So new velocity is old velocity plus (time interval * acceleration)

Exactly what I was thinking. So, torque=f(throttle, engine characteristics); thrust = f(torque, propeller characteristics, air density); drag = f(air density, pitch); lift = f(thrust, weight, drag). Did I get this right? Lift is then what, velocity in m/s?

For the force model: Torque = f(throttle, air density), drag = f(air density, speed squared, pitch), lift = f(air density, speed squared, pitch, flight path angle); if in trimmed flight and you fly faster, lift becomes > weight and the aircraft accelerates upward, causing the angle of attack to lower, which lowers lift. Lift and drag are forces, [N].

No need for trimmed flight. You use speed squared in drag and lift, but you mention no formula how to arrive at speed. From the torque I guess?

Well you start at a state where velocity is constant and no climb/descent, standstill on the runway for instance. Then apply throttle, which applies thrust, which accelerates the aircraft, and speed picks up until drag = thrust.

apply throttle, which applies thrust, which accelerates the aircraft, and speed picks up.<< So now we have the speed which we use in the rest of the equations you mentioned? >>Torque = f(throttle, air density), drag = f(air density, speed squared, pitch), lift = f(air density, speed squared, pitch, flight path angle); <<

Your problem is that those functions are not as simple as you may think. They are not linear.

@RoryAlsop Functions don't need to be linear for a numerical solution, see this answer. It's the method used on Full Flight Simulators, although at higher iteration rates than 1/sec.

Sorry - it was a not to Ska, not you Koyovis. I still think Ska thinks this should be simple, when it really isn't. :-)

There are a number of control inputs that are put in to get the aircraft climbing at a certain angle, or descending at a certain angle. If you know the airspeed of the aircraft in feet per second, you should be able to use trigonometry to calculate of that speed how much is horizonatal and how much vertical. The vertical component can then be used to adjust the altitude and the horizontal the position over the ground.
So you must constantly calculate altitude based on if the aircraft is climbing or descending just as you calculate position over the ground constantly as well.
I don't know how to translate control movements into trajectories, this would be dependent on speed again, for example at slower speeds you move the controls quite a long way to achieve a desired pitch angle where at higher speeds the controls are much more "firmer" and responsive.
Now add a bit of bank, or air currents, different aircraft, or the fact that real aircraft never quite fly straight and level, they move around a little, ever so slightly speeding up and slowing down, and it makes you realise why it would take a team of maybe a dozen some months if not years to produce something like Microsoft Flight Sim.
Even a simple model is complicated. Much easier to know how to fly an aeroplane than know how to write a simulator!
Hope this answer helps in some way. I don't wish to appear negative. Good luck!

As I stated in the question, I'm not trying to do full sim. Just a simplified model.

The key question you really have to answer yourself is how to simplyfy it? The point I was making was that altitutide and position over ground is related to speed and climb angle, and if you have these as key things you "know" then the simplification could come from how to get from torque, pitch etc, to speed and climb angle.

You can check my update in the question if that makes more sense.

To put it as simply as I know how, Climb/Descent is a function of engine power. At any given Attitude, the plane will fly at a specific Angle of Attack. The AOA determines the speed at which the wing will want to fly. With sufficient engine power, the airplane will fly that airspeed at a constant altitude. If more engine power is applied, the wing will attempt to fly at the same airspeed, and will climb at that airspeed. If less power is applied, the wing will attempt to fly at the same airspeed, and will descend. Adding the rate of acceleration induced climb/descent to the current altitude over time gives the new altitude. More simply, if a plane climbs at 100 feet per minute, it will be 100 feet higher after one minute.
This is the static condition. If left alone and not influenced by dynamic effects, this is what happens. Changes in engine power will result in a whole host of dynamic changes, but the wing will eventually settle itself down to the static case.


text:
Can I legally log PIC time in a high performance airplane without a high performance endorsement?
14 CFR 91.109(c) states, "No person may operate a civil aircraft in simulated instrument flight unless the other control seat is occupied by a safety pilot who possesses at least a private pilot certificate with category and class ratings appropriate to the airplane being flown"
I am a private pilot with a complex endorsement. My father's airplane is complex and high performance. Can I act as a safety pilot for him in his airplane as he shoots instrument approaches under foggles? And can I log this as PIC time? I have a certificate with category and class ratings (ASEL) appropriate to the airplane being flown, so why couldn't I?

You can act as a safety pilot, as long as you are rated in class and category. You can not log PIC time.
The usual way for a safety pilot to log PIC time is via 14 CFR § 61.51(e)(1)(iii):

When the pilot, except for a holder of a sport or recreational pilot certificate, acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted

Because you do not have an high performance endorsement, you cannot act as PIC and thus cannot log PIC time this way.
Instead, you can log SIC time per 14 CFR § 61.51(f)(2):

Holds the appropriate category, class, and instrument rating (if an instrument rating is required for the flight) for the aircraft being flown, and more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is being conducted

You can log PIC any time you are sole manipulator of the controls. If you are under the foggles while manipulating the controls, both you and your father can log PIC- you as sole manipulator under 61.51(e)(1)(i) and him as acting PIC under 61.51(e)(1)(iii).

You can act as a safety pilot but you cannot log PIC time.
Acting as the legal pilot in command and logging PIC time are two completely separate things.
You cannot act as the legal pilot in command without a high performance endorsement.

§61.31(f) Additional training required for operating high-performance airplanes.

(1) Except as provided in paragraph (f)(2) of this section, no person may act as pilot in command of a high-performance airplane (an airplane with an engine of more than 200 horsepower), unless the person has -

The rules for logging PIC time are found in §61.51(e).

Logging pilot-in-command flight time.

(1) A sport, recreational, private, commercial, or airline transport pilot may log pilot in command flight time for flights-

(i) Except when logging flight time under § 61.159(c), when the pilot is the sole manipulator of the controls of an aircraft for which the pilot is rated, or has sport pilot privileges for that category and class of aircraft, if the aircraft class rating is appropriate;
...
[iii] When the pilot, except for a holder of a sport or recreational pilot certificate, acts as pilot in command of an aircraft for which more than one pilot is required under the type certification of the aircraft or the regulations under which the flight is conducted; or

When you are acting as a safety pilot, you are a required crew member and can log the time in furtherance of higher grade certificates.  When you are the safety pilot and are logging that time as PIC you are using the stipulation in 61.51(e)(iii) and are saying you are legally responsible for the flight.  If there is an accident or incident, there will be precedent from your logbook (previous flight as safety pilot logging PIC) that you are legally responsible.
In this case, I would much prefer to log the time as SIC.  Since you do not have a high-performance endorsement, you cannot log PIC time as you do not qualify to act as the legal pilot in command per 61.31(f) and 61.51(e)(iii) and I would advise against logging PIC this way anyways.